The present invention relates in general to welding, and, more particularly, to devices for mounting a welding apparatus adjacent workpieces.
A connecting operation, such as welding or the like, is often used in the fabrication of many products, such as beams, or the like. Often, the welding operation is performed on workpieces which are being moved continuously past the welding station. Thus, a beam can be formed by welding a flange to a web as those elements move continuously past a welding torch.
A common manner of carrying out such a welding operation includes having the torch accurately positioned adjacent the location whereat the weld is to be placed, and precisely held in that position as the workpieces are moved thereby.
To effect a proper weld, the standoff distance, that is, the distance between the torch head and the weld point on the two surfaces to be welded together, must be precisely maintained. To accomplish this positioning, automatic tracking devices have been used.
Known tracking devices can be classified into two general groups. The first group includes those devices using contact type sensors. Those contact sensors have a mechanical device which moves electrical potentiometers. There are serious disadvantages to these contact type sensors. First, these devices are delicate and are easily damaged; second, these devices are subject to wear and must be frequently repaired. Furthermore, the actual position of the probe is critical to obtaining proper servo operation. If the probe angle of the sensor is not properly maintained, the servos are not properly responsive and proper action is inhibited, if not entirely prevented. The presence of foreign material on the weld surfaces may also seriously affect the operation of the contact type sensors. Such foreign material can include flux, which can contain fairly large granules of material.
A second group of tracking devices includes those devices using compressed air. These devices require standoff distances which are maintained to extremely close tolerances. Thus, a step change in material surface structures, such as a shoulder, or the like, is likely to cause a collision between the sensor and the material before that sensor can cause a change in position of the device. Such crashes can damage or destroy delicate instruments, necessitating expensive repairs and downtime. The compressed air used in these devices must be extremely clean, that is, entirely free of debris, such as dust, or the like. The cleanliness requirements are so strict as to require white room type conditions. Such specialized equipment is obviously expensive. It is also noted that a light granular flux cannot be used with sensors utilizing compressed air. The compressed air will blow the flux around, thereby causing difficulties. Furthermore, the presence of an air flow can distort the arc or the shielding gas on a gas arc.
Both types of known sensors are sensitive to electrical noise and any splattering caused by the welding operation. The adjustment of the standoff distance of known sensors is also quite difficult.